334 HISTORY OF CHRONOPHOTOGRAPHY. 



In certain fish the undulations take place in the lateral fins. The 

 ray (tig. 36, PI. VII) is shown in side view, swimming without advanc- 

 ing, its progress being impeded. The same fish seen from the front 

 has motions which strongly recall those of a Hying bird. 



Locomotion in the air. — Not only the night of birds, Imt that of 

 insects, studied by chronophotography, shows the details of its 

 mechanism. The extreme rapidity of these motions — several hundred 

 per second — requires extremelv short exposures. To avoid any defect 

 of sharpness due to the velocity of the wing, the writer has reduced 

 the duration of the n\*sh to less than one twenty-thousandth of a second. 

 Only isolated photographs have been obtained, but even these are 

 highly instructive. Fig. 37 (PI. VII) is a motionless crane-fly; fig. 38 

 (PI. VII) shows it in night. The torsion of the wing under the resist- 

 ance of the air, a phenomenon which theory had predicted, and which 

 explains the mechanism of insect flight, is shown in the picture. 



Functional motion*. — Independently of acts of locomotion, the dif- 

 ferent parts of the body execute various movements, the observation 

 of which is in some cases excessively difficult. In speech and in mas- 

 tication the lower jaw takes displacements that one would not have 

 anticipated. The ribs, in respiration, rise and separate in a way that 

 was of old unknown. In certain joints the bones move about a fixed 

 center, while in others there is a rolling motion of the condyles over 

 the surface in contact with them. Chronophotography on the dead- 

 black background gives a drawing to scale of all these motions. 

 Bright lines or points fixed to the organ under examination interpret 

 the trajectory upon the photographic plate. 



Thus the motions of the lower jaw in the act of opening the mouth 

 are represented (tig. ;*>'.». PI. VIII) by those of a rod bent at an angle 

 and forced to move with the jaw. It will lie seen that the motion is 

 not a rotation round the joint, but takes place about instantaneous 

 centers in the upright branch, while the condyle itself slides over the 

 surface of the glenoid cavity, which is convex downward. 



In respiration bright points fixed upon the ribs are displaced with 

 the latter and interpret the motions of the rising ribs on a circular arc. 



The heart of an animal, laid bare and brilliantly illuminated, gives on 

 the moving film the succession of systole and diastole of its auricles and 

 ventricles. The motions of the eyes themselves have been studied at 

 the physiological station by M. Orchansky. He has chronophoto- 

 graphed the dotted trajectory of the eyes in reading, and in this motion 

 has been able to distinguish the components, due respectively to the 

 ocular muscles and to the displacements of the head. 



Motions of the air in the utterance oftJu vowt Is. — The eminent phys- 

 icist, R. Koenig, conceived the idea of making the sonorous vibrations 

 due to instruments or to the voice act upon capsules with membranous 



